Conventionally, a vehicle-mounted HC measurement device described in JP Published Patent Application No. 2004-117259 A (Patent Document 1) is available as an exhaust gas analyzer for car or the like. This vehicle-mounted HC measurement device is adapted to allow a NDIR (non-dispersive infrared spectroscopy) gas analyzer, an exhaust gas flowmeter and an arithmetic operation circuit to be installed in a vehicle, the NDIR for continuously measuring a HC (hydrocarbon) concentration in exhaust gas flowing through an exhaust tube connected with an engine, the exhaust gas flowmeter continuously measuring a flow rate of the exhaust gas flowing through the exhaust tube, and the arithmetic operation circuit performing arithmetic operation of an output from the NDIR gas analyzer and an output from the exhaust gas flowmeter to continuously calculate a THC (total hydrocarbon) amount in the exhaust gas.
Although the above-stated exhaust gas analyzer described in Patent Document 1 can facilitate measuring the THC in exhaust gas of a vehicle when the vehicle is moving on a real road, it is impossible to conduct analysis of the exhaust gas in real time because the exhaust gas has to be transferred for analysis of gas components from the exhaust path of the engine to an analysis section through a pipe. Further, in order to reduce the above-described units in size, analysis is carried out only for a limited component such as HC. At the development stage of an engine or attachments to the engine such as an exhaust gas purifier, it has been desired to provide an exhaust gas analyzer facilitating the measurement of components other than hydrocarbon in exhaust gas, such as nitrogen oxides and carbon monoxide, while being capable of measuring a component of the exhaust gas or a gas concentration in real time.
Then, the applicant of the present invention has developed a gas analyzer capable of facilitating the measurement of even a large number of gas components in gas such as nitrogen oxides and carbon monoxide in real time. FIG. 7 illustrates the gas analyzer.
A sensor unit 72 includes a through hole 73 formed at a center thereof, and includes reflecting mirrors 74, 74 opposed to each other to sandwich the through hole 73 therebetween. This sensor unit 72 is disposed in a gas flowing path such as an exhaust tube connected with an engine, and is configured so that gas flowing through the through hole 73 of the sensor unit 72 is emitted with laser light.
A laser diode 70 emits laser light of a wavelength band including a wavelength absorbed by a gas component to be measured, and the emitted laser light is guided to a demultiplexer 71 via an optical fiber 81 and is demultiplexed by the demultiplexer 71 into measurement laser light and reference laser light. The thus demultiplexed measurement laser light is guided to an emission unit of the sensor unit 72 via an optical fiber 82, and is applied to gas flowing in the through hole 73 through the emission unit. While the measurement laser light applied to the gas is reflected a plurality of times between the reflecting mirrors 74, 74, the laser light of a specific wavelength is absorbed by a gas component contained in the gas, so as to be received by a photoreceiver 75. The received measurement laser light is converted into an electric signal 85 by the photoreceiver 75, and the electric signal 85 is output to a difference detector 77 and an I/V converter 80. The electric signal 85 input to the I/V converter 80 is I/V converted by the I/V converter 80, and is further converted into a digital signal by an A/D converter 78, which is then input to an analyzer (computer) 79 as a measurement received-light intensity signal.
On the other hand, the reference laser light is guided to a photoreceiver 76 via an optical fiber 83, and is received by the photoreceiver 76 to be converted into an electric signal 86. The electric signal 86 is output to the difference detector 77. The difference detector 77 calculates a difference between the electric signal 85 for the measurement laser light that has passed through the gas and the electric signal 86 for the reference laser light that does not pass through the gas. The calculated differential signal is converted into a digital signal by the A/D converter 78, and is output to the analyzer (computer) 79.
Based on the differential signal input by the difference detector 77 and the electric signal 85 from the photoreceiver 75 indicating the measurement received-light intensity, the analyzer 79 finds an absorption spectrum (standardized absorption spectrum) when the measurement laser light of a predetermined intensity passes through the gas. The analyzer 79 compares the calculated absorption spectrum with a theoretical spectrum for analysis to measure a concentration of a gas component contained in the gas as well as a temperature and a pressure of the gas.
Patent Document 1: JP Published Patent Application No. 2004-117259 A